Hi, crashbars can be had yes, i know KEDO - Performance Products
offers some, aswell as others.
I have a 23ltr acerbis tank on, and dont have crashbars, but I didnt have crashbars with the stock fueltank either. When I crash, i sometimes bend the brakepedal or the gearshifter, but they are easy to bend back. Id rather have that, than having them snap.
K&N filter on the xt600e should require many carb issues, as the bikes come rich from stock. But i wouldnt reccomend them for dusty conditions, most people wont. I have a pipercross (piperx) foamfilter for mine.
I would have valuables in a tank bag og backpack, and always carry it with me.
I have a yamaha rack, its only rated for like 5kg ( i guess better safe than sorry) but i've had much more weight on it with no issues. One could reinforce it a bit to make it attach to the subframe aswell...
As for the ammobox, i dont know, a small one could be handy i guess.As long as it doesnt go up over the cylinder, i guess you should be fine.
Aftermarket footpegs from a yamaha tw200 fit directly, and they often cost aorund 15$ on ebay or at Motorcycle Parts | Motorcycle Accessories | Motorcycle Gloves | D2Moto
Hope this helps.